1. Field of the Invention
The present invention relates to a pneumatic tire and, more specifically, to a pneumatic tire capable of drastically reducing an eccentric fitting amount relative to a rim.
2. Description of the Related Art
Generally, a carcass layer of a pneumatic tire is configured to be fastened by folding both ends respectively around a pair of left and right bead cores. In this way, by fastening the carcass layer by folding the both ends thereof around the bead cores, it is possible to avoid the ends of the carcass layer from being pulled out of the bead cores when an unvulcanized tire is pressed against an inner surface of a mold from inside by inflating a bladder during vulcanization forming, and to provide carcass cords with uniform tension in order to improve uniformity of the tire.
However, the carcass layer is formed by winding a belt-shaped carcass material in a circumferential direction of the tire and then by splicing the both ends to be overlapped. Accordingly, such spliced portions constitute highly rigid bumps on an inner circumferential surface (an inner diameter side) of each of the bead cores, which is almost formed into a completely round shape. Such bumps would increase a primary eccentric fitting component when the tire is mounted on a rim, and may sometimes cause abnormal vibration when a vehicle is running.
Concerning this problem, as disclosed in Patent Documents 1 and 2, it is possible to prevent protrusion of the bumps of the spliced portions on the inner circumferential surface of the bead core by means of splitting the bead core in two and interposing the end of the carcass layer therebetween instead of folding the end around the bead core. However, when an unvulcanized tire simply configured to interpose the end of the carcass layer between the split portions of the bead core is subjected to vulcanization with a bladder inflation type vulcanizer, the end of the carcass layer may sometimes be pulled out of the bead core when the unvulcanized tire is pushed upward by the bladder. For this reason, it is not possible to employ the vulcanizing method utilizing the bladder inflation for vulcanizing this pneumatic tire. Instead, it is necessary to employ a method of assembling the unvulcanized tire on a surface of a rigid core mold and subjecting the assembled unvulcanized tire directly to thermal vulcanization as disclosed in Patent Document 3.
Nevertheless, in the vulcanizing method using the rigid core mold, it is necessary to form the unvulcanized tire so as to strictly equalize the tension among the carcass cords on the surface of the rigid core mold. Otherwise, widths of ends of the carcass cords to be interposed between the split portions of the bead core may become uneven after thermal contraction of the cords, and uniformity of the tire is thereby deteriorated. Accordingly, this method requires tremendous operations for managing the tension of the carcass cords. As a result, overall operability is substantially reduced and manufacturing costs are increased.
(Patent Document 1) Japanese unexamined patent publication No. 6(1994)-171306
(Patent Document 2) Japanese unexamined patent publication No. 7(1995)-215006
(Patent Document 3) Japanese unexamined patent publication No. 62(1987)-270308